As circuit dimensions shrink the need for fine-line lithography becomes more critical and the requirements for planarizing topography becomes very severe. Major semiconductor companies are actively pursuing Chemical-Mechanical Polishing (CMP) as the planarization technique used in the sub-half micron generation of chips. CMP is used for planarizing bare silicon wafers, interlevel dielectrics, and other materials. CMP machines, such as the one shown in FIG. 1, use orbital, circular, lapping motions. The wafer 16 is held on a rotating carrier 18 while the face of the wafer 16 being polished is pressed against a resilient polishing pad 14 attached to a rotating platen disk 12. A slurry 20 is used to chemically attack the wafer surface to make the surface more easily removed by mechanical abrasion.
As CMP stands today it is a very costly process to implement. One of the major costs of running CMP are the `consumables`. These include polishing pads, polishing slurry, wafer backing pads and various machine parts which are worn out during polishing. The polishing pads represent a major cost, as much as five dollars per product wafer run. In highly integrated devices utilizing multilevel interconnect systems each wafer can use five or six CMP steps. This makes the cost for polishing pads alone $25 to $30 per wafer.
These polish pads are worn out from both the polishing process and the pad conditioning which is necessary to make the pad ready for wafer polishing. The pad conditioning is currently done by mechanical abrasion of the pads in order to `renew` the surface. During the polishing process, particles removed from the surface of the wafer and from the spent slurry become embedded in the pores of the polishing pad. This reduces the effectiveness of the polishing pad. Conditioning removes depleted slurry from surface and opens pores in the pad which were blocked by particles. The open pores provide more surface area for polishing with new slurry. Current techniques, such as the one shown in FIG. 1 use conditioning heads 24 with abrasive diamond studs 26 which are macroscopic in relation to the cells in the polishing pad. Thus, the mechanical abrasion of the polishing pads wears the pad, reducing its lifetime. In addition, the diamond studs 26 are not evenly distributed over the surface of the conditioning head. This causes uneven conditioning.